This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. This study will utilize advanced imaging methods to elucidate the neurophysiological mechanisms underlying the clinical effects of pedunculopontine nucleus deep brain stimulation in patients with Parkinson's disease. In addition to providing valuable information regarding normal brain function and how this is altered in Parkinson's disease, the proposed study will provide practically useful information regarding patient selection for this procedure in clinical practice.